Which statement is true about salts of alkali metals potassium, sodium, and lithium?

• A. They are insoluble
• B. They are soluble
• C. Only potassium salts are soluble
• D. They are volatile

Answer: (B)

Solubility of salts in water depends on the balance between lattice energy (the strength holding the solid together) and hydration energy (water’s ability to surround and stabilize the ions). Salts formed from alkali metals have a +1 charge and relatively low lattice energy, so water can disrupt the crystal structure easily. At the same time, these small, highly charge-dense cations (Li+, Na+, K+) are strongly hydrated by water. The combination means the ions are stabilized in solution rather than in the solid lattice, so these salts dissolve readily.

That’s why salts of lithium, sodium, and potassium are soluble in water. They’re not insoluble, and they aren’t volatile, so the statement about their solubility being true fits.